Siloxane boundary lubricants



' Patented June 16, 1953 .7

Dow GorningjCorporation, Midland, Mich., a corporation of Michigan I No Drawing. Application February 8, 1952,

Serial No. 270,771 6Clain1s. (Cl.252 -37.2)

This invention relates to novel siloxane lubricants having improved high pressure character. tics, eminently suitable as boundary lubricants.

Siloxane lubricantsof this invention comprise liquid halogenated arylsiloxane copolymers. of the general formula where n has an average value of more than 2 and less than 3 and R is methyl, ethyl, phenyl and halogenated aryl, to which has been added from 0.01 to 5 per cent by weight (based on the siloxane) of copper, magnesium or lead in the form of their salt of aliphatic carboxylic acids having from 4 to 9 carbon atoms or salt of cyclohexyl derivatives of such aliphatic acids.

Modern high speed power machinery units require lubricants capable of maintaining a lubricant film between tightly pressed shearing surfaces. Compositions designed for such purposes are known as high'pressure or boundary lubricants Ordinary petroleum oils per se are generally unsuited for high pressure conditions so it has been found necessary to add substances such as sulfur and phosphorus compounds to adapt them to the requirements of boundary lubrication. Although many excellent petroleum boundary lubricants have been developed, they are, in all cases, subject to the temperature limitations of their petroleum base. Thus, at elevated temperatures oxidation occurs and at low temperatures freezing or congealing takes place both of which quickly destroy all lubricating properties. I

In the last decade fluid siloxane lubricants have been developed which are stable attemperatures from below -50 C. to above 150 C. These siloxane lubricants have replaced petroleumwherever extreme temperature conditions have so required. The siloxane lubricants comprising the main methyl, ethyl, and phenylmethyl siloxane units aregenerally poorly suited (in comparison with their petroleum counterpart) for boundary or high pressure lubrication, particularly where steel surfaces are involved. Considerable improvement has been made in siloxane boundary lubricants by employing halogenated arylsilox anes as described in the pending application of Fletcher et al., Serial No. 115,783, filed September 14, 1949, now U. S. Patent 2,599,984, assigned to the same assignee as this application.

It is the object of this invention to prepare fluid siloxane lubricants having superior high pressure characteristics and therefore more suit- 2 I able as boundary lubricants at ordinary and extreme temperatures. v

This invention resides in a lubricating composition or mixture composed of a liquid halogenated aryl copolymer towhich has been added a copper, lead, 'o'r magnesium salt of certain fatty acids. The addition of such fatty acid salts brings about important, critical and unexpected improvement in siloxane fluid lubricants. This improvement manifests itself when such siloxane lubricants are exposed to high pressure conditions,

The siloxane copolymers suitable for use are described and claimed in the pending application of Herbert J. Fletcher heretofore referred to. Such siloxanes are those having the general formula I wherein R is methyl, phenyl, and halogenated phenyl or xenyl radicals and n has an average value greater than 2 and less than 3. The halogenated aryl radicals may contain from 1 to 7 chlorine or bromine atoms each and are present on the siloxane chain in sufficient amount and are halogenated to such an extent that the ratio of the halogen atoms to silicon atoms is from 0.5 to 5. The remaining radicals attached to the silicon may be methyl or phenyl but at least 37 per cent of the R radicals in the siloxane are methyl. a

1 Such siloxane copolymers may be prepared'by several methods. For example, halogenated aryl- 'chlorosilanes may be cohydrolyzed and cocondensed with methyland 'phenylchlorosilanes. The halogenated arylchlorosilanes may be conveniently prepared by direct halogenation of arylchlorosilanes in the presence of FeCh as catalyst.

The metallic salts suitable for use consist of copper, lead, or magnesium salts of aliphatic carboxy acids having from 4' to 9 carbon atoms inclusive, such as butyric, nonylic, caproic, Z-ethylhexanoic, and cyclohexyl-substituted. aliphatic acids such as cyclohexylnonylic, cyclohexylbutyric, cyclohexyl ca'proic and cyclohexylvaleric.

These metallic salts may be prepared in the usual manner by reacting an aqueous alcohol solution of the sodium salt with compounds such as copper nitrate, magnesium nitrate or lead nitrate. Thus, for example, caproic acid is dissolved in alcohol and neutralized Withaqueous NaOI-I. The alcoholic solution is heated to about 80 and .an equivalence of copper nitrate added whereby copper caproate precipitates out of solution. Particularly preferred are the copper, lead or magnesium salts of Z-ethylhxanoic acid since they are readily available commercially. Most beneficial results have been realized by employin copper 2-ethylhexoate.

Additives well known in the lubrication art such as anti-corrosion agents or anti-oxidants may be added to the mixtures of this invention. The lubricantsof this invention may also be readily compounded with fillers such as the alkali metal salts or alkali earth metal salts of fatty acids to produce greases having superior high pressure characteristics.

In some instances considerable effort may be required to prepare homogeneous mixtures of the salt and the siloxane by mechanic means alone. It is therefore convenient and time saving to employ small amounts of a mutual solvent. The solvents, which are thereby present in the mixture in small amounts percentagewise, may

be removed if desired by heating or other suitable means, but such is not necessary. Aliphatic carboxy acids as defined supra are preferred as solvents for the metallic salts since commercial preparations are available which contain the metal salt dissolved in its own acid. Solutions in the range of equal parts by weight of salt and solvent to those having 4 parts solvent to 1 part salt are recommended. Any large excess of solvent over the foregoing, however, should be avoided unless it is subsequently removed.

The metallic salts are added to the siloxane in such amount that the per cent by weight of the metal based on the siloxane amounts to .01 to 5.0, preferably .1 to 3.0. The objects of this invention are enjoyed only in part or not at all if larger amounts of metallic fatty acid salts are employed.

The mixtures or compositions of this invention were tested on a Falex Lubricant Testing Machine. This machine is well known in the lubrication'industry and from it may be obtained measurements which accurately express the ability of a lubricant to prevent wear between moving metal parts under pressure. The operation and nature of the Falex machine is described by Victor A. Ryan in Lubrication Engineering; September 1946; pp. 102 to 104.

Essentially the test involves rotating a shaft between two V-blocks as pressure is applied to the bearing surface. The resulting wear of the shaft and the V-blocks when operated under a given load and for a given period of time is measured by means of a ratchet-wheel. The wear is expressed in teeth wear, one tooth wear being equal to .0000556 inch of wear in depth.

The lubricants of this invention were tested at room temperature in accordance with the following test:

The Falex machine, employing steel V-blocks and steel shaft, is started and a load of 50 pounds gage is applied in a machine run of 5 minutes. At the end of this period load loss is noted and tooth wear is measured. The load is readjusted to 50 pounds (to compensate for load loss if any), and a machine run for a second 5 minutes is made after which the above observations are again noted. Next a 100 pound load is applied over two5 minute intervals observing load loss and tooth wear in each interval as before.

In the table the total load loss and tooth Wear of the 4 intervals mentioned in the preceding paragraph are totaled. Since both load loss and tooth wear are essential for proper evaluation of the lubricant, a factor consisting of their prod not has been included in the table to make comparison more clear.

EXAMPLE 1 The following mixtures were prepared employing fluid chlorinated arylsiloxane copolymer having 'a composition of 6 mol per cent 5 mol per cent CsHsCI-IzSiO, 14 mol per cent (CH3)3SiO1 2, and 75 mol per cent (CH3)2SiO. Metallic salts, dissolved in fatty acids in a 1:2 ratio, were added to the siloxane and dispersed therein with the aid of laboratory stirrers. The

' amount of salt added is tabulated on the basis of per cent by weight metal based on the siloxane.

Mix Pegent tum Additive Solvent Weight Metal 1. 2. Copper 2 ethylhexoate- .Z-cthyl hexanoic acid 2 3.- do do 1 4 O w.(10 0 25 5 Copper cyclohexyl Oyclohexyl caproic 0.5

caproa-te, acid. Lead 2-ctliyl heroata. Z-cthyl hexanoic acid 0. 25 Magnesium 2ethyl 0. 25

hcxoate. 8. Copper butymte Butyric acid 0. 5

L Load loss and tooth wear Load=50 pounds for 10 minutes and pounds for 10 minutes] Load LossX Mixture Load Loss Tooth I Tooth Wear 100 77 68 52. 3G 25 29 7. 25 7 7 (l. 49 2 6 0. 12 12 .9 l. 08 39 36 14. 04 57 63 35. 9 55 51 28. 05

In the table, the superiority of the compositions of this invention are quite obvious. The degree of improvement ranges up to more than four hundred fold as shown in column 3.

EXAMPLE 2 When the metallic salts of Example 1 are added in the manner of Example 1 to a fluid brominated arylsiloxane copolymer having "a composition of 6 mol per cent BT2C12H'1SiO3 2, 5 mol per cent CeHsCI-IaSiO, 14 mol per cent (CHsnSiOuz and 75 mol per cent (CHa)2SiO, lubricants are produced having the improved characteristics shown in the table.

That which is claimed is:

l. A composition of matter consisting essentially of (1) a liquid copolymeric siloxane having a degree of substitution of greater than 2 and less than 3 organic radicals per silicon atom, said siloxane containing halogenated aryl radicals selected from the group consisting of halogenated phenyl radicals and halogenated xenyl radicals,

said radicals having substituted thereon from 1 to 7, inclusive, halogen atoms selected from the group consisting of chlorine and bromine, the remaining organic radicals in said siloxane selected from the group consisting of methyl and phenyl radicals, in which siloxane the halogenated aryl radicals are present in amount so that the ratio of halogen atoms to silicon atoms is from .05 to and in which siloxane at least 37 per cent of the total number. of organic radicals are methyl radicals and (2) from .01 to 5 per cent by weight based on (1) of a metal selected'from the group consisting of copper, magnesium, and lead, said metal being present in the form of the salt of an acid selected from the group consisting of aliphatic carboxy acids having 4 to 9 carbon atoms, inclusive, and cyclohexyl derivatives of such aliphatic acids.

2. The composition of claim 1 wherein the metal is present in the form of a salt of 2-ethylhexanoic acid.

3. The composition of claim 1 wherein copper is present in the form of copper 2-ethy1hexoate.

4. A composition of matter consisting essentially of (1) a liquid copolymeric siloxane having a degree of substitution of greater than 2 and less than 3 organic radicals per silicon atom, said siloxane containing halogenated aryl radicals selected from the group consisting of halogenated phenyl radicals and halogenated xenyl radicals, said radicals having substituted thereon from 1 to 7, inclusive, halogen atoms selected from the group consisting of chlorine and bromine, the remaining organic radicals in said siloxane selected from the group consisting of methyl and phenyl radicals, in which siloxane the halogenated aryl radicals are present in amount so that the ratio of halogen atoms to silicon atoms is from .05 to 5 and in which siloxane at least 37 per cent of the total number of organic radicals are methyl radicals and (2) from 0.1 to 3 per cent by Weight based on (1) of a metal selected from the group consisting of copper, magnesium, and lead, said metal being present in the form of a salt of an acid selected from the group consisting of aliphatic carboxy acids having 4 to 9 carbon atoms, inclusive, and cyclohexyl derivatives of such aliphatic acids.

5. The composition of ,claim 4 wherein the metal is present in the form of a salt of 2-ethylhexanoic acid.

6. The composition of claim 4 wherein copper is present in the form of copper 2-ethylhexoate.

CHESTER C. CURRIE.

References Cited in the file of this patent UNITED STATES PATENTS Fletcher et al. June 10, 1952 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF (1) A LIQUID COPOLYMER SILOXANE HAVING A DEGREE OS SUBSTITUTION OF GREATER THAN 2 AND LESS THAN 3 ORGANIC RADICALS PER SILICON ATOM, SAID SILOXANE CONTAINING HALOGENATED ARYL RADICALS SELECTED FROM THE GROUP CONSISTING OF HALOGENATED PHENYL RADICALS AND HALOGENATED XENYL RADICALS, SAID RADICALS HAVING SUBSTITUTED THEREON FROM 1 TO 7, INCLUSIVE, HALOGEN ATOMS SELECTD FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE, THE REMAINING ORGANIC RADICALS IN SAID SILOXANE SELECTED FROM THE GROUP CONSISTING OF METHL AND PHENYL RADICALS, IN WHICH SILOXANE THE HALOGENATED ARYL RADICALS ARE PRESENT IN AMOUNT SO THAT THE RATIO OF HALOGEN ATOMS TO SILICON ATOMS IS FROM .05 TO 5 AND IN WHICH SILOXANE AT LEAST 37 PER CENT OF THE TOTAL NUMBER OF ORGANIC RADICALS ARE METHYL RADICALS AND (2) FROM .01 TO 5 PER CENT BY WEIGHT BASED ON (1) OF A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, MAGNESIUM, AND LEAD, SAID METAL BEING PRESENT IN THE FORM OF THE SALT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC CARBOXY ACIDS HAVING 4 TO 9 CARBON ATOMS, INCLUSIVE, AND CYCLOHEXYL DERIVATIVES OF SUCH ALIPHATIC ACIDS. 